Light emitting device, and method for manufacturing thereof

ABSTRACT

A method for manufacturing a light emitting device includes: roughening a light extracting surface of a semiconductor light emitting element, forming a first light transmissive layer on an entirety of the roughened light extracting surface, flattening a surface of a first light transmissive layer that is on a side opposite the semiconductor light emitting element, forming a second light transmissive layer on an entirety of a surface of an optical member, flattening a surface of the second light transmissive layer that is on a side opposite the optical member, and directly bonding the flattened surface of the first light transmissive layer and the flattened surface of second transmissive layer by performing surface-activated bonding, atomic diffusion bonding, or hydroxyl bonding.

BACKGROUND OF THE INVENTION Field of the Invention

The present disclosure relates to a light emitting device which uses asemiconductor light emitting element, and a method for manufacturingthereof.

Description of the Related Art

A semiconductor light emitting element (or a light emitting diode; LED)has the following features in comparison with an electric light bulb: a)a response speed for turning on and turning off is faster, b) a lengthof life is 50th to 100th times longer, and c) an electric powerconsumption is about ⅓ to about 1/15. By applying such features, a lightemitting device which uses the semiconductor light emitting element isutilized in a very wide range of fields such as a back light of a liquidcrystal display, an outdoor full color display, a toy, a generallighting, a light source for reading and/or writing of an opticalrecording medium, a light source for optical communication and the like.It is also expected to facilitate energy saving by using the LED, andcurrently, study and development of the LED is energetically performed,aiming at raising luminance, efficiency or the like. In particular,relating to the light emitting devices for automobile use, and forgeneral lighting use, the demand for a high luminance, a high efficiencyand a low electric power consumption is very strong.

Under such circumstances, an invention for enhancing a light extractingefficiency from a light emitting device is described in JP2012-124219A.In JP2012-124219 A, there is disclosed an invention relating to asemiconductor light emitting element which has a semiconductor laminatedstructure having a light emitting layer placed between a firstconductive type layer (an n-type semiconductor layer) and a secondconductive type layer (a p-type semiconductor layer), and in which alight is extracted from the first conductive type layer side of a lightemitting layer. In the light emitting device according toJP2012-124219A, a surface (a light extracting surface) of the firstconductive type layer, which surface is opposite to another surfacewhich contacts the light emitting layer is roughened to suppress totalreflection of the light emitted from the light emitting layer, resultingin enhancement of light extracting efficiency.

As described in the JP2012-124219A, the light emitting device in whichthe light extracting surface of the first conductive type layer isroughened might be one preferred embodiment for enhancing the lightextracting efficiency.

SUMMARY OF THE INVENTION

However, when the light extracting surface of the first conductive typelayer is roughened, there is a problem that the light emitting elementcannot be bonded to an optical member such as a lens, a wavelengthconverting member or the like while keeping the enhanced lightextracting efficiency. In other words, if the optical member isconnected onto the roughened first conductive type layer, a void (thatis, a layer of air having a low refractive index) is generated atboundary faces between them because the surface of the first conductivetype layer is roughened. If the void exists, a partial or totalreflection of the light (hereinafter, simply called “total reflection”)is caused by the Fresnel reflection due to difference in a refractiveindex between the first conductive type layer and air, leading tosuppression of the light extracting efficiency. While the void is notgenerated by connecting the first conductive type layer and the opticalmember with using an adhesive agent, the total reflection is likely tobe generated to reduce the light extracting efficiency at each boundaryface thereof because the refractive indexes of the first conductive typelayer, the adhesive agent and the optical member are different from eachother.

One aspect of the present invention is made to overcome theabove-mentioned conventional problem, and aims at providing a lightemitting device having an enhanced light extracting efficiency, and amethod for manufacturing the same.

A light emitting device according to one aspect of the present inventionis a light emitting device comprising an optical member provided on alight extracting surface side of a semiconductor light emitting elementvia a first light transmissive layer, wherein,

bonding surfaces of said semiconductor light emitting element and saidfirst light transmissive layer are roughened surfaces;

bonding surfaces of said first light transmissive layer and said opticalmember are flat; and

said first light transmissive layer and said optical member are directlybonded.

A method for manufacturing a light emitting device according to anotheraspect of the present invention is a method for manufacturing a lightemitting device comprising an optical member provided on a lightextracting surface side of a semiconductor light emitting element via afirst light transmissive layer, the method comprising the steps of:

(i) roughening a light extracting surface of said semiconductor lightemitting element;

(ii) forming said first light transmissive layer on said roughened lightextracting surface;

(iii) flattening an upper surface of said first light transmissivelayer; and

(iv) directly bonding said flattened upper surface of said first lighttransmissive layer and a surface of said optical member.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view of a light emitting deviceaccording to an embodiment of the present invention.

FIG. 2 is a schematic sectional view describing relationship amongpropagation of a light, internal multiple reflection of a light andabsorption of a light when a first light transmissive layer is formed.

FIG. 3 is a schematic sectional view describing relationship amongpropagation of a light, internal multiple reflection of a light andabsorption of a light when a first light transmissive layer is notformed.

FIG. 4 is a schematic sectional view describing a phenomenon observedwhen a light emitting element and an optical member are connected withusing a resin material such as an adhesive agent or the like.

FIG. 5 is a schematic sectional view describing a phenomenon observedwhen a light emitting element and an optical member are directly bonded.

FIG. 6 is a schematic sectional view describing an optical member formedof a non-uniform material.

FIG. 7 is a schematic sectional view of a light emitting deviceaccording to another embodiment of the present invention.

FIG. 8 is a schematic sectional view of a light emitting deviceaccording to a variation of the embodiment of the present invention.

FIG. 9 is a schematic sectional view of a light emitting deviceaccording to a variation of the embodiment of the present invention.

FIG. 10 is a schematic sectional view of a light emitting deviceaccording to a further embodiment.

FIG. 11 is a flowchart describing a method for manufacturing a lightemitting device according to an embodiment of the present invention.

FIG. 12A is a schematic sectional view describing a step of forming anLED, which is included in a method for manufacturing a light emittingdevice according to an embodiment of the present invention.

FIG. 12B is a schematic sectional view describing a step of attaching asupporting substrate, which is included in the method for manufacturinga light emitting device according to the embodiment of the presentinvention.

FIG. 12C is a schematic sectional view for describing a step of removinga growth substrate, which is included in the method for manufacturing alight emitting device according to the embodiment of the presentinvention.

FIG. 12D is a schematic sectional view describing a polishing step,which is included in the method for manufacturing a light emittingdevice according to the embodiment of the present invention.

FIG. 12E is a schematic sectional view describing a step of roughening asurface, which is included in the method for manufacturing a lightemitting device according to the embodiment of the present invention.

FIG. 12F is a schematic sectional view describing a step of forming afirst light transmissive layer, which is included in the method formanufacturing a light emitting device according to the embodiment of thepresent invention.

FIG. 12G is a schematic sectional view describing a step of flattening afirst light transmissive layer, which is included in the method formanufacturing a light emitting device according to the embodiment of thepresent invention.

FIG. 12H is a schematic sectional view describing a chipping stepperformed after the step of flattening a first light transmissive layer,which is included in the method for manufacturing a light emittingdevice according to the embodiment of the present invention.

FIG. 12I is a schematic sectional view describing a bonding step, whichis included in the method for manufacturing a light emitting deviceaccording to the embodiment of the present invention.

FIG. 12J is a schematic sectional view describing a step for removing asupporting substrate, which is included in the method for manufacturinga light emitting device according to the embodiment of the presentinvention.

FIG. 12K is a schematic sectional view describing a cutting step, whichis included in the method for manufacturing a light emitting deviceaccording to the embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

A light emitting device and a method for manufacturing thereof accordingto embodiments of the present invention will be described accordingly,with referring to the accompanying drawings.

(Light Emitting Device)

At first, a light emitting device according to the embodiment will bedescribed with referring to FIG. 1 .

The light emitting device illustrated in FIG. 1 is an example of an LEDchip for flip-chip mounting (face-up mounting) in which an n-sideelectrode 2 n and a p-side electrode 2 p are provided on one surfaceside of a semiconductor stack 3. In FIG. 1 , the light emitting device 1is flip-chip mounted such that a surface on which the n-side electrode 2n and the p-side electrode 2 p are formed (hereinafter called “theelectrode forming surface”) faces downward, and a light is emittedupward from a surface which is opposite to the electrode forming surfaceof the semiconductor stack 3. The technical idea of the presentdisclosure is, however, not limited to the above construction, and canbe applied to the light emitting device 1 for wire mounting (face-upmounting).

As illustrated in FIG. 1 , the light emitting device 1 includes asemiconductor light emitting element 4 (hereinafter, simply called“light emitting element 4”), a first light transmissive layer 5, and anoptical member 6.

More specifically, the light emitting device 1 includes the opticalmember 6 which is provided on a light extracting surface 41 side of thelight emitting element 4 via the first light transmissive layer 5. Thus,the light emitting device 1 is configured such that the first lighttransmissive layer 5 and the optical member 6 are laminated in thisorder on the light extracting surface 41 of the light emitting element4. In the present embodiment, bonding surfaces of the light emittingelement 4 and the first light transmissive layer 5 are roughenedsurfaces, and bonding surfaces of the first light transmissive layer 5and the optical member 6 are flattened surfaces. In the specification,the “light extracting surface” means a surface of the semiconductorstack 3, which surface is opposite to the surface on which the n-sideelectrode 2 n and the p-side electrode 2 p are formed (an upper surfaceof the n-type semiconductor layer 31 in FIG. 1 .) The “bondingsurface(s)” means comprehensively surfaces of two different objects (forexample, elements or members) at a bonding portion where the surfaces ofthe two objects are bonded. Therefore, the “bonding surfaces of thelight emitting element and the first light transmissive layer” indicateboth the surface of the light emitting element and the surface the firstlight transmissive layer, and the “bonding surfaces of the first lighttransmissive layer and the optical member” indicate both the surface ofthe first light transmissive layer and the surface of the opticalmember.

(Light Emitting Element)

The light emitting element 4 includes the semiconductor stack 3, then-side electrode 2 n and the p-side electrode 2 p. The light emittingelement 4 emits a light by recombination of electrons and positive holesprovided from the n-side electrode 2 n and the p-side electrode 2 prespectively in the semiconductor stack 3. The semiconductor stack 3 asillustrated in FIG. 1 is configured such that a n-type semiconductorlayer 31, an active layer 32, and a p-type semiconductor layer 33 arelaminated in this order from the light extracting surface 41 of thelight emitting element 4. The active layer 32 is also called a lightemitting layer, and the active layer 32 may be formed optionally. Then-type semiconductor layer 31 is connected to the n-side electrode 2 n,and the p-type semiconductor layer 33 is connected to the p-sideelectrode 2 p.

The layers forming the semiconductor stack 3 may be preferably obtained,for example, by epitaxially growing the n-type semiconductor layer 31,the active layer 32, and the p-type semiconductor layer 33 in this orderon a growth substrate such as sapphire. All of these layers arepreferably formed of one or more elected form the group consisting ofGaN, GaAs, InGaN, AlInGaP, GaP, SiC, ZnO and the like. In particular,for these layers, it is preferable to use a GaN compound which isrepresented by a general formula In_(X)Al_(Y)Ga_(1-X-Y)N (0=<X, 0=<Y,X+Y<1).

Each of the n-type semiconductor layer 31, the active layer 32 and thep-type semiconductor layer 33 may have a single layer construction, alayered construction composed of two or more layers which have differentcompositions and film thicknesses, a superlattice construction or thelike. In particular, the active layer 32 preferably has a single quantumwell structure or a multiple quantum well structure, which includes athin membrane generating the quantum effect. In such a quantum wellstructure, the well layer is preferably a nitride semiconductorincluding “In”.

As illustrated in FIG. 1 , the light extracting surface 41 of the lightemitting element 4 is a surface on the side which does not contact theactive layer 32, in the n-type semiconductor layer 31. As mentionedabove, the n-type semiconductor layer 31 may be formed using GaN or thelike. Since a refractive index of GaN is so high such as about 2.5,total reflection is likely to be generated at the boundary face betweenthe light extracting surface 41 and the outside when a light isextracted from the light extracting surface 41. Therefore, as mentionedabove, the light extracting surface 41 (the surface which contacts thefirst light transmissive layer) is roughened in this light emittingelement 4. According to such construction, the light extracted from thelight extracting surface 41 can be scattered, and thereby suppressingthe total reflection. Consequently, the light extracting efficiency ofthe light emitting device 1 can be enhanced. Also opportunities of themultiple reflection in the semiconductor stack 3 can be reduced, wherebythe light extracting efficiency of the light emitting device 1 can befurther enhanced. Judgment whether the light extracting surface 41 is aroughened surface or not is made according to the comparison whether thelight extracting surface 41 is rougher than the below-mentioned bondingsurfaces of the first light transmissive layer 5 and the optical member6, or not.

The light extracting surface 41 may be roughened with a wet process (awet etching) with using an alkaline solution or the like, or a dryprocess (a dry etching). The light extracting surface 41 may beroughened by forming dotted patterns or line and space patterns. Thelight extracting surface 41 may also be roughened by combining thepattern formation with the wet process or the dry process.

The roughened surface may be configured such that convex portions orconcave portions whose dimensions and shapes are not constant areformed, or such that convex portions or concave portions whosedimensions and shapes are constant are placed randomly or in regularly.The light extracting surface 41 is a roughened surface whose arithmeticaverage roughness Ra is preferably greater than 50 nm, and morepreferably greater than 150 nm. The arithmetic average roughness Ra canbe determined according to the JIS B0601-2001.

In FIG. 1 , the n-side electrode 2 n and the p-side electrode 2 p arelocated apart from each other with a predetermined distance to avoidelectrical connection, on the lower side of the semiconductor stack 3.Thus, the n-side electrode 2 n and the p side electrode 2 p are providedindependently from each other.

The n-side electrode 2 n and the p-side electrode 2 p are formed of ametal electrode material, similarly to a conventional light emittingelement. The metal electrode material is, for example, at least one oralloy thereof selected from the group consisting of, for example, Au,Cu, Ni, Al, Pt, Cr, Rh and the like. Each of the n-side electrode 2 nand the p-side electrode 2 p may be formed in a single layer or amultilayered film. Both of the n-side electrode 2 n and the p-sideelectrode 2 p may be formed as a multilayered film in which a Cu singlelayer or a Cu/Ni layered film is placed as a lower layer and Au or AuAsalloy is formed thereon as an upper layer. Each of the n-side electrode2 n and the p-side electrode 2 p may be formed by sputtering, vapordeposition or the like.

The p-side electrode 2 p is preferably connected to the p-typesemiconductor layer 33 via the whole-area electrode 2 p 1 which diffusesan electric current in in-plane uniform manner toward the p-typesemiconductor layer 33. Accordingly, it is preferable that thewhole-area electrode 2 p 1 is an ohmic electrode which can give a goodelectrical connection to the p-type semiconductor layer 33. Thewhole-area electrode 2 p 1 also functions as a reflective layer toreflect a light emitted by the semiconductor stack 3 toward the lightextracting surface 41. Therefore, the whole-area electrode 2 p 1 ispreferably formed of a material which has a high reflectance at leastrelative to the wavelength of the light emitted by the active layer 32.The whole-area electrode 2 p 1 is preferably a single layer film whichis formed of Ag or alloy thereof which has a high reflectance relativeto the light, or a multilayered film in which a film of theabove-mentioned Ag or alloy thereof is placed as a lowest layer, and afilm formed of Ni and/or Ti or the like is provided thereon.

In particular, when Ag is used for a material of the whole-areaelectrode 2 p 1, it is preferable to provide a covering electrode 2 p 2which covers the whole-area electrode 2 p 1. The covering electrode 2 p2 diffuses an electric current in the entire surface of the p-typesemiconductor layer 33, similarly to the whole-area electrode 2 p 1.Further, the covering electrode 2 p 2 covers an upper surface and sidesurfaces of the whole-area electrode 2 p 1 to block off the whole-areaelectrode 2 p 1, and thereby preventing the contact between thewhole-area electrode 2 p 1 and the p-side electrode 2 p. In other words,the covering electrode 2 p 2 functions as a barrier layer for preventingthe migration of the material of the whole-area electrode 2 p 1,especially Ag. The covering electrode 2 p 2 is formed of, for example,one kind of metal or alloy thereof selected from the group consisting ofTi, Au, W, Al, Cu and the like. The covering electrode 2 p 2 may be asingle layer film or a multilayered film. Specifically, the coveringelectrode 2 p 2 may be a single layer film formed of AlCu ally, AlCuSialloy or the like, or a multilayered film including such a film. Each ofthe whole-area electrode 2 p 1 and the covering electrode 2 p 2 may beformed by sputtering, vapor deposition or the like.

In the light emitting element 4, an exposed surface of the side wherethe electrodes are formed is preferably covered with a protecting layer7, except for the end surfaces of the n-side electrode 2 n and thep-side electrode 2 p. In the light emitting element configured in theabove-mentioned manner, the protecting layer 7 is, in particular, formedon the surface of the semiconductor stack 3, on the upper surface of thecovering electrode 2 p 2, at the periphery of the n-side electrode 2 n,and at the periphery of the p-side electrode 2 p. It is preferable thatthe protecting layer 7 is formed of, for example, at least one selectedfrom the group consisting of oxides of Si, Ti, Ta, Nb, Zr, Mg and thelike (for example, SiO₂, TiO₂, Ta₂O₂, Nb₂O₅, ZrO₂, MgO), a Si nitride(for example, Si₃N₄), a nitride such as AlN etc., a magnesium fluorideMgF₂ and the like. In the case of using the above-mentioned materials,the protecting layer 7 may be formed by sputtering, vapor deposition orthe like.

(First Light Transmissive Layer)

A first light transmissive layer 5 is formed on the upper surface 31 ofthe n-type semiconductor layer 31 of the semiconductor stack 3, that is,on the light extracting surface 41 of the light emitting element 4. Thefirst light transmissive layer 5 may have dielectric property. The firstlight transmissive layer 5 propagates a light extracted from the lightextracting surface 41 in the layer and emits the light from a surface ofthe opposite side (this surface may be called “light emitting surface51” in the specification).

The first light transmissive layer 5 is preferably formed of, forexample, at least one inorganic dielectric material selected from thegroup consisting of SiO₂, SiON, TiO₂ and Al₂O₃, or an organic-inorganichybrid material containing at least one selected from the groupconsisting of SiO₂, SiON, TiO₂ and Al₂O₃ as an inorganic component. Theabove-mentioned inorganic dielectric material may be formed by CVD(Chemical Vapor Deposition), sputtering, vapor deposition, ALD (AtomicLayer Deposition) or the like. Examples of the organic component used inthe organic-inorganic hybrid material include polyethylene,polypropylene, polystyrene, nylon, polycarbonate, polyethyleneterephthalate, polyimide and the like. The organic-inorganic hybridmaterial may be formed by a sol-gel process, an in-situ polymerisationprocess, a solid-phase reaction method or the like. While the preferredmaterials for the first light transmissive layer 5 are exemplifiedabove, the material for the first light transmissive layer 5 is notlimited to them. For example, the first light transmissive layer 5 maybe formed of any material having a light transmissive property relativeto the wavelength of the light emitted by the light emitting element 4,and having the refractive index that is almost the same as that of theoptical member 6 to which the first light transmissive layer 5 isbonded.

Since the first light transmissive layer 5 after being formed isflattened by polishing, it is preferable that the layer 5 is formed tohave a thickness enough to exceed a concavo-convex portion of the n-typesemiconductor layer 31 existing before the layer 5 is formed. In otherwords, the first light transmissive layer 5 is preferably formed withthe thickness enough to cover the concavo-convex portion of the lightextracting surface 41 so that the concavo-convex portion dose not appearon a surface of the layer 5. The thickness of the first lighttransmissive layer 5 may be, for example, 100 nm to 1000 nm.

A refractive index of the first light transmissive layer 5 is preferablyat the same level as that of the refractive index of the semiconductorstack 3 which contacts the first light transmissive layer 5, or at thesame level as that of the refractive index of the optical member 6. Ifthe refractive index of the first light transmissive layer 5 is the sameas the refractive index either of the layer or the member which is incontact with the first light transmissive layer 5, the refractive-indexboundaries can be reduced. Accordingly, it is possible to reduce thetotal reflection which is generated at the boundary face between thesemiconductor stack 3 and the first light transmissive layer 5, or atthe boundary face between the first light transmissive layer 5 and theoptical member 6, and thereby enhancing light extracting efficiency. The“at the same level” means, for example, that difference in refractiveindex between the first light transmissive layer 5 and the semiconductorstack 3 or the optical member 6 is within a range of ±0.3 based on anabsolute value, preferably within a range of ±0.1, and furtherpreferably within a range of ±0.05.

As the difference in refractive index between the first lighttransmissive layer 5 and the semiconductor stack 3 is smaller, therefraction of the light emitted from the light emitting element 4 isless likely to arise and therefore the effect given by roughening thelight extracting surface 41 is less likely to be obtained. On the otherhand, since the first transmissive layer 5 and the optical member 6 aredirectly bonded to form a relative flat interface, the light extractingefficiency may be reduced due to the influence of refraction when thedifference in refractive index between both layers is large. For thesereasons, the refractive index of the first light transmissive layer 5 ismore preferably at the same level as the refractive index of the opticalmember 6.

Specifically, the refractive index of the first light transmissive layer5 may be about 1.4 to about 2.0, especially about 1.6 to about 2.0. Ifthe refractive index of the first light transmissive layer 5 is withinthis range, the total reflection generated in any of the above-mentionedboundary faces can be suppressed more certainly, and thereby enhancingthe light extracting efficiency more certainly. If the refractive indexof the first light transmissive layer 5 exceeds 2.0, there is a casethat it is difficult to enhance the light extracting efficiency since alight tends to be absorbed more. The refractive index of the first lighttransmissive layer 5 can arbitrarily be adjusted according to theselection of the material, the condition to form the layer and the like,with considering the light transmittance. The refractive index of SiO(specifically, for example SiO₂) is 1.41, the refractive index of SiN(specifically, for example Si₃N₄) is 2.0, and the refractive index ofSiON (also generally called SiO_(x)N_(y)) is between the above-mentionedvalues. Accordingly, when the first light transmissive layer 5 is formedby CVD or the like, by adequately setting a content ratio of Si, O andN, it is possible to make the refractive index at the same level as thatof the refractive index of the semiconductor stack 3, or at the samelevel as that of the refractive index of the optical member 6.

The light emitting surface 51 of the first light transmissive layer 5 isbonded to a surface 61 of the optical member 6. The bonding of thesesurfaces is preferably performed by direct bonding. In the presentspecification, the “direct bonding” or “directly bonded” means bondingwithout application of an adhesive agent or another resin. Examples ofthe direct bonding include surface-activated bonding, atomic diffusionbonding, hydroxyl bonding or the like. One of the above-mentionedmethods may be selected and utilized when the light emitting surface 51and the surface 61 are bonded. All of these bondings can be performed bya normal temperature bonding method performed under the normaltemperature.

The surface-activated bonding is a method wherein an impurity such as anoxide, moisture, an organic substance or the like, which is attached tosurfaces of members that are objects to be bonded, is removed togetherwith a part of the surface layer thereof, and then bonding hands ofatoms on the surfaces are bonded directly under the normal temperature.This method is disclosed in WO 2011/126000, which is incorporated byreference in its entirety.

The atomic diffusion bonding is a method wherein a micro crystal filmsuch as Al or the like is formed on each of the surfaces of memberswhich are objects to be bonded (that is, surfaces which become bondingsurfaces after bonding) under the super high vacuum condition, and thenthe formed thin films are bonded by lamination under the vacuumcondition.

The hydroxyl bonding is a method wherein each of the surfaces of membersthat are objects to be bonded is subjected to a hydrophilicizingtreatment to form a hydroxyl group (OH group) thereon, and the surfacesare brought into contact with each other to bond hydroxyl groups byhydrogen bonding.

If the first light transmissive layer 5 and the optical member 6 aredirectly bonded, the first light transmissive layer 5 and the opticalmember 6 can be bonded strongly. Further, as understood from FIG. 2 andFIG. 3 , the thickness of the light propagating layer can be increasedby forming the first light transmissive layer 5. Consequently, in thelight emitting device 1, it is possible to reduce opportunities forabsorption of the light by the electrodes when internal multiplereflections occur, and thereby enhancing the light extractingefficiency.

When the first light transmissive layer 5 and the optical member 6 aredirectly bonded, it is not necessary to use a resin, such as an adhesiveagent, of which refractive index is significantly different from thoseof the layer 5 and the member 6. Since refractive index of the resinsuch as the adhesive agent or the like is about 1.43 to 1.53, the totalreflection is likely to arise at the boundary face between a resin 8 andthe light emitting element 4 (see FIG. 4 ). On the contrary, the presentembodiment prevents the generation of the total reflection by directlybonding the first light transmissive layer 5 and the optical member 6 inorder to avoid substantial interposition of the adhesive layer such asthe resin 8 or the like. In the light emitting device 1, since the resinmaterial such as the adhesive agent or the like is not used, differencein the refractive index between the semiconductor stack 3 and theoptical member 6 can be reduced. Therefore, the light emitting device 1can enhance the light extracting efficiency.

The light emitting device according to the present embodiment is apreferred one in the view of the quality control, the manufacturingprocess, the product quality and the product reliability. In the lightemitting device 1, when the first light transmissive layer 5 and theoptical member 6 are bonded using the resin 8 such as the adhesive agentor the like, there is a possibility that the adhesive agent 8 hangs downor spills over from the edge portion of the bonding surfaces, asillustrated in FIG. 4 . If the adhesive agent 8 hangs down, thecharacteristic of the products cannot be stabilized. Therefore, thedevice or the process for removing the adhesive agent 8 which hangs downis required for the quality control. If the adhesive agent 8 spills overand then hangs down beyond the lowest part of the dice (the lightemitting element 4) to reach the mounting part of the dice, there is arisk that the mounting strength, thus the reliability of products willbe adversely affected. In the light emitting device 1 according to thepresent embodiment, since the first light transmissive layer 5 and theoptical member 6 are directly bonded without using the adhesive agent,the inconvenience caused by the hanging of adhesive agent is avoided.Accordingly, the light emitting device 1 of the present embodiment is apreferred one in the view of the quality control and the manufacturingprocess, and the product quality and the product reliability can beenhanced.

In the light emitting device 1, since the first light transmissive layer5 and the optical member 6 are directly bonded, it is possible toproduce a dice which has a thickness exceeding the thickness capable ofbeing divided by scribing or the dicing. In addition, for example, ifthe light emitting device 1 is used as an ultraviolet (UV) LED, thedeterioration of the resin 8 (such as an adhesive agent) is never causedby the ultraviolet light (see FIGS. 4 and 5 ), and thereby enhancing thereliability of products. Since the UV LED often emits a light from thelight emitting element to the air directly, the total reflection likelyto occur at the boundary face which contacts the air, and therebyextremely lowering the light extracting efficiency. In the lightemitting device of the present embodiment, however, since the firstlight transmissive layer 5 and the optical member 6 that is directlybonded thereto cover the light emitting element 4, the device 1 has aconstruction like a light emitting diode provided with a resin mold.Therefore, the present embodiment gives a UV LED which significantlyenhances the light extracting efficiency in comparison with a UV LEDwhich emits ultraviolet light to the air directly.

A description will be continued with going back to FIG. 1 . In order tobond the first light transmissive layer 5 and the optical member 6 well,it is required that both the upper surface of the first lighttransmissive layer 5 (that is, the principal surface which is exposedafter the layer 5 is formed) and the surface of the optical member 6which is to be bonded to the first light transmissive layer 5 are flat.If the flatness of these surfaces is not enough, the above-mentioneddirect bonding cannot be performed. In the case where the flatness ofthese surfaces is low, a void (that is, a layer of an air whose refractindex is low) is generated at the interface therebetween, and therebylowering light extracting efficiency even if these surfaces are directlybonded. The bonding surfaces of the first light transmissive layer 5 andthe optical member 6 become flat surfaces by the bonding of flatsurfaces.

Both the upper surface (the light emitting surface 51) of the firstlight transmissive layer 5 and the surface 61 of the optical member 6preferably have a flatness such that the arithmetic average roughness Rais 1 nm or less. In order to obtain such flatness, for example, aflattening process using the CMP (Chemical Mechanical Polishing) methodmay be applied to the light emitting surface 51 of the first lighttransmissive layer 5 and/or the surface 61 of the optical member 6. Thearithmetic average roughness Ra can be determined according to the JIS B0601-2001.

(Optical Member)

The optical member 6 is, as mentioned above, provided on the lightemitting surface 51 of the first light transmissive layer 5, andpreferably bonded to the light emitting surface 51 by the directbonding. The direct bonding is preferably performed with the normaltemperature bonding method. The optical member 6 has a function to exerta predetermined effect on a light emitted from the light emittingsurface 51 of the first light transmissive layer 5. Examples of such anoptical member 6 include a fluorescent plate, a sapphire substrate, aGaN substrate, a lens and the like, but not limited thereto. A materialof the optical member 6 is not limited particularly as long as it has alight transmissive property relative to the wavelength of the lightemitted from the light emitting element 4.

In the case of using the fluorescent plate as the optical member 6, afluorescent material is included in the optical member 6. Thefluorescent material absorbs at least a part of the light extracted fromthe semiconductor stack 3, and converts the wavelength thereof to alight having a different wavelength. Since color of the light obtainedby combining the light emitted from the semiconductor stack 3 and thelight emitted from the fluorescent material becomes the color of thelight emitted from the light emitting device 1, the fluorescent materialor the like is selected in order to obtain a light of desired colortone. The fluorescent material may be at least one selected from thegroup consisting of an oxide, a nitride, an oxynitride and the like forgeneral use. Examples of such fluorescent material include a YAG-basedfluorescent material in which YAG (Yttrium-Aluminum-Garnet) is activatedby Ce or the like, and a nitride-based fluorescent material and anoxide-based fluorescent material which are activated by a lanthanideselements such as Eu, Ce and the like. The fluorescent plate may beformed of an inorganic material such as glass or the like which issintered together with the fluorescent material.

In the case of using the sapphire substrate as the optical member 6, thesapphire substrate may be a flat plate member. In the case of using theGaN substrate as the optical member 6, a GaN substrate may be a flatplate member. If any of these substrates is bonded to the first lighttransmissive layer 5, a thickness of the light propagating layer in thelight emitting device 1 can be increased. Accordingly, the number of themultiple reflections of the light can be reduced in the light emittingdevice 1, and thereby suppressing the light containment and the lightabsorption.

The refractive index of the optical member 6 is preferably at the samelevel or the same as the refractive index of the first lighttransmissive layer 5. If the refractive index of the optical member 6exceeds 2.0, there is a case that it is difficult to enhance the lightextracting efficiency since a light tends to be absorbed more.

In the case of using the lens as the optical member 6 (refer to FIG. 8as described below), the lens may be formed of sapphire, GaN, a glass, aresin or the like, and may include a fluorescent material. By using thelens as the optical member 6, it can refract a light, and therebyconcentrating or diffusing the light. The lens may be a convex lens asillustrated in FIG. 8 , or may be a concave lens.

If the optical member 6 is formed with using a material which is nothomogeneous such as a fluorescent plate 64 in which a fluorescentmaterial 63 is included in an inorganic material 62 such as glass or thelike, there is a case that it is difficult to make the arithmeticaverage roughness Ra 1 nm or less in spite of using the CMP method orthe like. This is because a polishing rate is different according to acomponent of the material.

Accordingly, the following is preferable in the case of using theoptical member 6 as mentioned above. For example, as illustrated in FIG.7 , it is preferable to provide a second light transmissive layer 9having a flat surface 91 on the surface of the optical member 6 whichfaces the first light transmissive layer 5. The second lighttransmissive layer 9 may be formed similarly to the first lighttransmissive layer 5. Thus, the second light transmissive layer 9 may beformed of, for example, at least one inorganic dielectric materialselected from the group consisting of SiO₂, SiON, TiO₂ and Al₂O₃, or anorganic-inorganic hybrid material including, as an inorganic component,at least one selected from the group consisting of SiO₂, SiON, TiO₂ andAl₂O₃.

In the case of providing the second light transmissive layer 9, thesurface 91 which becomes the bonding surface after being bonded to thefirst light transmissive layer 5 has preferably a flatness such that thearithmetic average roughness Ra is 1 nm or less, as well as the lightemitting surface 51 of the first light transmissive layer 5. The firstlight transmissive layer 5 and the second light transmissive layer 9which have such flat surfaces may be directly bonded by the normaltemperature bonding method or the like. Such flatness can suppressgeneration of the void at the interface between the first lighttransmissive layer 5 and the second light transmissive layer 9. In thecase of providing the second light transmissive layer 9 on the opticalmember 6, since the void is hardly formed at the interface between thesecond light transmissive layer 9 and the optical member 6, the lightemitting device 1 with very few voids over its entirety can be obtainedas a result. Therefore, in the case of using the second lighttransmissive layer 9, the total reflection due to the void can besuppressed in the light emitting device 1, and thereby enhancing thelight extracting efficiency.

Since the second light transmissive layer 9 may be formed of thematerial which is similar to that of the first light transmissive layer5, the refractive index of the second light transmissive layer 9 can beat the same level or the same as the refractive index of the first lighttransmissive layer 5. Accordingly, the total reflection is hardlygenerated at the interface between the first light transmissive layer 5and the second light transmissive layer 9, and therefore the lightextracting efficiency is not lowered. Further, when the first lighttransmissive layer 5 and the second light transmissive layer 9 areformed of the same material, the total reflection due to the differenceof the refractive index of the material can be prevented, and thethickness of the light propagating layer can be increased. Therefore,the use of the second light transmissive layer 9 can give the lightemitting device 1 in which the light extracting efficiency is enhanced,even if the surface of the optical member 6 is not flat. Since the firstlight transmissive layer 5 and the optical member 6 are integrated bythe direct bonding also in the light emitting device 1 having the secondlight transmissive layer 9, the bonding strength thereof is high and theeffect of enhancing the reliability can be obtained by avoiding the useof the adhesive agent.

The first light transmissive layer 5 and the second light transmissivelayer 9 are preferably bonded by the direct bonding because of the samereason as described relating to the bonding between the first lighttransmissive layer 5 and the optical member 6, and more preferably bythe surface-activated bonding, the atomic diffusion bonding or thehydroxyl bonding.

The light emitting device 1 having the above-described construction canemit a light by recombination of electrons provided by the n-sideelectrode 2 n and the n-type semiconductor layer 31, and positive holesprovided by the p-side electrode 2 p and the p-type semiconductor layer33 in the active layer 32. The semiconductor stack 3 has the lightextracting surface 41 from which a light can be extracted. The lightextracted from the light extracting surface 41 of the semiconductorstack 3 propagates in the first light transmissive layer 5, and isemitted from the light emitting surface 51 located at the opposite side.The light emitted from the light emitting surface 51 enters the opticalmember 6 and then is emitted to the outside of the light emitting device1. In the light emitting device 1 according to the present embodiment,since the light emitting surface 51 of the first light transmissivelayer 5 and the bonding surface 61 of the optical member 6 are flat andboth surfaces are directly bonded, there can be suppressed the totalreflection which is generated due to the difference in the refractiveindex between the adhesive agent and the semiconductor, or due to thevoid. As a result, the light extracting efficiency of the light emittingdevice 1 can be enhanced. Specifically, when the light emitting surface51 of the first light transmissive layer 5 and the surface 61 of theoptical member 6 are flattened respectively and directly bonded, thelight extracting efficiency can be enhanced by 10% in comparison withthe case that the first light transmissive layer 5 and the opticalmember 6 are adhered with using a silicone resin (refractive indexn=1.53).

(Variation of Light Emitting Device)

As mentioned above, in the light emitting device 1 as described mainlyreferring to FIG. 1 , the plate-like member (for example, thefluorescent plate or the like) is bonded as the optical member 6 ontothe light emitting surface 51 of the first light transmissive layer 5.In the following description, as a variation, a light emitting deviceusing another optical member is described. The same reference numberswill be applied to the members or elements which have already beendescribed, and further description thereof will be omitted.

As illustrated in FIG. 8 , in a light emitting device 1 a of a variationof the present embodiment, a lens is bonded as an optical member 6 ontothe light emitting surface 51 of the first light transmissive layer 5.As mentioned above, in the light emitting device 1 a, a light emittedfrom the light emitting surface 51 of the first light transmissive layer5 can be concentrated or diffused by the lens.

As illustrated in FIG. 9 , in a light emitting device 1 b of anothervariation of the present embodiment, a fluorescent flat plate 6 a, as anoptical member 6, is bonded onto the light emitting surface 51 of thefirst light transmissive layer 5, and a lens 6 b is further bonded, asthe optical member 6 onto the fluorescent flat plate 6 a. In the lightemitting device 1 b, a light having desired color tone can be obtainedby the fluorescent flat plate, and the light of the desired color tonecan be concentrated or diffused by the lens. In the embodiment asillustrated in FIG. 9 , the bonding of the fluorescent flat plate 6 a orthe like and the lens 6 b may be made by the direct bonding, or byanother means such as using the adhesive agent or the like. Heating maybe optionally performed during the bonding.

(Light Emitting Device According to Another Embodiment)

Next, a light emitting device according to another embodiment isdescribed with referring to FIG. 10 . The light emitting device asillustrated in FIG. 10 is one aspect of the light emitting device, forexample, used for a back light of a liquid crystal display, an outdoorfull color display, a toy, a general lighting, a light source foroptical communication and the like. In the following description, thelight emitting device according to the present embodiment is called “alight source device 10” for convenience of the explanation.

As illustrated in FIG. 10 , the light source device 10 is provided witha light emitting device 1 mounted on a mounting substrate 11, a sealingmember 12 which seals the light emitting device 1. The light emittingdevice 1 is configured in the same manner as that described withreferring to FIG. 1 .

The light emitting device 1 is mounted on the mounting substrate 11 byconnecting each of electrodes of the light emitting device 1 (an n-sideelectrode 2 n and a p-side electrode 2 p) to a wiring 14 of the mountingsubstrate 11 via a bump 13.

The mounting substrate 11 may be a conventional substrate used formounting of an LED, and not limited particularly as long as it enablesthe LED to be mounted thereon.

The sealing member 12 may be formed of, for example, a material selectedform the resin material such as epoxy resin and silicone resin, and aninorganic material such as glass. A method to seal the light emittingdevice 1 is not limited particularly. For example, the sealing member 12may be formed with using a compression molding method or a transfermolding method, which uses a metal mold. Alternatively, a potting methodmay also be applied in which a bank is provided at any part (forexample, at an outer edge) of the mounting substrate 11 and a materialfor the sealing member 12 which has an adequate viscosity is droppedthereon. The sealing member 12 preferably has a light transmissiveproperty relative to the light emitted by the light emitting device 1,and if necessary, it may include a light diffusing element, a heatconductive element or a fluorescent material which converts wavelengthof the light.

The bump 13 may be, for example, a plated bump such as an Au bump, asolder bump, a Cu pillar bump and the like, an Au stud bump, a solderprinted bump or the like.

As described above, the light emitting device 10 of the presentembodiment is provided with the light emitting device 1 as mentionedabove. In the light emitting device 1, as mentioned above, since thelight emitting surface 51 of the first light transmissive layer 5 andthe surface 61 of the optical member 6 are flat and thereby forming theflat bonding surfaces, there can be suppressed the total reflectionwhich is generated due to the difference in refractive index between theadhesive agent and the semiconductor, or due to the void. Consequently,the light extracting efficiency can be enhanced also in the case of thelight emitting device 10 wherein the light emitting device 1 isemployed.

[Manufacturing Method of Light Emitting Device]

A method for manufacturing a light emitting device according to anembodiment of the present invention (hereinafter it may simply be called“a manufacturing method”) will be described with referring to FIG. 11and FIGS. 12A to 12K.

The manufacturing method according to the present embodiment is amanufacturing method of a light emitting device in which an opticalmember 6 is provided on a light extracting surface 41 side of a lightemitting device 4 via a first light transmissive layer 5.

As illustrated in FIG. 11 , a minimum configuration of the manufacturingmethod of the present embodiment consist of a step of roughening asurface S5, a step of forming a first light transmissive layer S6, astep of flattening a first light transmissive layer S7, and a bondingstep S8. In this manufacturing method, the above-mentioned steps areperformed in the above-mentioned order to manufacture theabove-mentioned light emitting device 1.

In a manufacturing method according to a more detailed and preferableembodiment, a step of forming an LED S1, a step of attaching asupporting substrate S2, a step of removing a growth substrate S3, and apolishing step S4 are performed. Subsequently to the steps S1 to S4, theabove-mentioned steps from the step of roughening a surface S5 to thebonding step S8 are performed, followed by a step of removing asupporting substrate S9 and a cutting step S10.

In FIGS. 12A to 12D, the preceding steps which are performed before thestep of roughening a surface S5, are illustrated. In FIGS. 12E to 12I,the steps from the step of roughening a surface S5 to the bonding stepS8 are illustrated. In FIG. 12I, the step of removing a supportingsubstrate S9 is illustrated, and in FIG. 12K, the cutting step S10 isillustrated.

The more detailed and preferable embodiment of the manufacturing methodwill be described with referring to FIGS. 12A to 12K together with FIG.11 . It goes without saying that the minimum configuration of themanufacturing method is included in the detailed embodiment. Therefore,the detailed embodiment will be herein after described in place of theexplanation of the minimum configuration of the manufacturing method.

The steps from the step of forming an LED S1 to the polishing step S4which are performed before the step of roughening a surface S5, aresteps of obtaining the light emitting element 4 in which the lightextracting surface 41 is flattened, which becomes the object to beroughened at the step of roughening a surface S5. Since these steps aregeneral steps for manufacturing a light emitting element, the contentswill be described briefly with referring to FIG. 11 and FIGS. 12A to12D.

(Step of Manufacturing LED)

As illustrated in FIG. 11 and FIG. 12A, the step of manufacturing an LEDS1 is a step where the semiconductor stack 3 is formed by laminating then-type semiconductor layer 31, the active layer 32 and the p-typesemiconductor layer 33 (all of them are not shown in FIG. 12A, see FIG.1 ) in this order on a growth substrate 20, and then predeterminedelectrodes are formed thereon.

In the specific description with referring to FIG. 1 , the n-typesemiconductor layer 31, the active layer 32 and the p-type semiconductorlayer 33 are laminated sequentially on the growth substrate 20.Subsequently, photolithography and etching are performed for removing apart of the p-type semiconductor layer 33, the active layer 32 and then-type semiconductor layer 31, whereby the n-type semiconductor layer 31is exposed at the position where the n-side electrode 2 n is to beformed and a concave portion for separation of the light emittingelement is formed. Then, the n-side electrode 2 n is formed on thebottom surface of the exposed n-type semiconductor layer 31. The p-sideelectrode 2 p is formed on a predetermined position of the p-typesemiconductor layer 33. It is preferable to form the protecting layer 7during this step. A sapphire substrate or the like may preferably beused as the growth substrate 20. It is preferable to measure thecharacteristics of the LED at this moment.

(Step of Attaching a Supporting Substrate)

Next, as illustrated in FIGS. 11 and 12B, the step of attaching asupporting substrate S2 is a step wherein a substrate for support (asupporting substrate 22) is attached with using a resin 21 onto the sidewhere the n-side electrode 2 n and the p-side electrode 2 p are formed.

The supporting substrate 22 may be, for example, a carrier plate ofsapphire or a carrier plate with a through-hole.

It is preferable that the resin 21 may be removed by the wet process(the wet etching) or the dry process (the dry etching), and have highresistance properties against high temperature, or against acid andalkalis. As such resin material, for example, a polyimide-based resinmay be exemplified.

(Step of Removing a Growth Substrate)

As illustrated in FIGS. 11 and 12C, the step of removing a growthsubstrate S3 is a step wherein the growth substrate 20 (not illustratedin FIG. 11C, see FIG. 12B) is removed from the light emitting element 4formed on the growth substrate 20.

The growth substrate 20 may be removed by a method wherein a laser lightwith the wavelength that is absorbed by the material (for example, GaNor the like) which forms n-type semiconductor layer 31, is applied fromthe side of the growth substrate 20 (a laser lift off (LLO)). Since thelight emitting device 1 according to the present disclosure is of aconfiguration having no growth substrate 20, it is not necessary to takecare of the light (a blue light in the case of blue LED) emitted fromthe side surface of the growth substrate 20.

(Polishing Step)

Next, as illustrated in FIGS. 11 and 12D, the polishing step S4 isperformed. The polishing step S4 is a step wherein a stripped surface 4a of the light emitting element 4, which surface is exposed by theremoval of the growth substrate, is polished. In the present embodiment,the polishing is performed for the separation of the light emittingelement 4 (more specifically, the semiconductor layers) at the concaveportion formed during the LED forming step. The polishing is performedsuch that the bottom of the concave portion is removed by polishing.

Such polishing process may be performed, for example, by the CMP method,or by using a grinder and a polisher. If the light emitting device 1 tobe manufactured is used for an ultraviolet LED, it is preferable toremove an initial growth layer of the semiconductor stack 3, whichabsorbs an ultraviolet light.

At the stage when the above-mentioned step of removing a growthsubstrate S3 is completed, separation between the chips has not beenperformed. Therefore, if the separation is necessary, a chipping processmay be performed after this polishing step S4 is completed. The chippingprocess may be performed by scribing or by dicing.

When the above-mentioned steps are performed, the stripped surface 4 awhich is polished (this surface corresponds to the light extractingsurface 41 of the light emitting element 4) is to be roughened (see FIG.11 and FIG. 12E) in the step of roughening a surface S5 as describedbelow,

(Step of Roughening a Surface)

As illustrated in FIGS. 11 and 12E, the step of roughening a surface S5is a step wherein the light extracting surface 41 of the light emittingelement 4 is roughened.

In the step of roughening a surface S5, a predetermined process isperformed to the light emitting element 4 having the light extractingsurface 41 which is to be flattened (or the stripped surface 4 a whichhas been polished in the polishing step S4).

The predetermined process is, for example, the wet process (the wetetching) with using an alkaline solution, the dry process (the dryetching) or the like. According to these processes, the light extractingsurface 41 of the light emitting element 4 can be roughened in theself-organizing manner. The step of roughening a surface is not limitedto those, but it may be, for example, a process employing a grinderand/or a polisher. Alternatively, the step of roughening a surface S5may be a step of forming dotted patterns or line and space patterns bythe photolithography and the etching and so on. Alternatively, the stepof roughening a surface S5 may be a step wherein the step of formingdotted patterns or line and space patterns and the wet process or thedry process are combined.

(Step of Forming a First Light Transmissive Layer)

As illustrated in FIGS. 11 and 12F, the step of forming a first lighttransmissive layer S6 is a step wherein the first light transmissivelayer 5 is formed on the light extracting surface 41 which has beenroughened.

As mentioned above, the first light transmissive layer 5 is formed of,for example, an inorganic dielectric material, or an organic-inorganichybrid material. A forming method of the first light transmissive layer5 may be selected from the CVD, the sputtering, the vapor deposition,the ALD, the sol-gel process, the in-situ polymerisation process, thesolid-phase reaction method and so on, depending on the materials.

(Step of Flattening a First Light Transmissive Layer)

As illustrated in FIGS. 11 and 12G, the step of flattening a first lighttransmissive layer S7 is a step wherein the upper surface of the firstlight transmissive layer 5 is flattened. The upper surface of the firstlight transmissive layer 5 flattened in this step becomes the lightemitting surface 51.

The flattening of the upper surface of the first light transmissivelayer 5 may be performed, for example, by the CMP method. The flatteningprocess is preferably performed such that the arithmetic averageroughness Ra becomes 1 nm or less.

If the chipping needs to be performed before the bonding step S8, thechipping process may be performed after the step of flattening a firstlight transmissive layer S7 is completed (see FIG. 12H). The chippingprocess may be performed, for example, by the scribing or by the dicing.

(Bonding Step)

As illustrated in FIGS. 11 and 12I, the bonding step S8 is a step ofbonding the upper surface (the light emitting surface 51) of the firstlight transmissive layer 5 which has been flattened, and the surface 61of the optical member 6 which has been flattened.

It is preferable to flatten the surface 61 of the optical member 6,which surface is to be bonded to the first light transmissive layer 5,before the bonding step S8. If the surface 61 of the optical member 6 issufficiently flat, it is not necessary to subject the surface 61 to theflattening process. As mentioned above, the arithmetic average roughnessRa of the surface 61 of the optical member 6 is preferably 1 nm or less.Therefore, when the flattening process is performed, the flatteningprocess is preferably performed such that the arithmetic averageroughness Ra becomes 1 nm or less.

As mentioned above, it is preferable that the light emitting surface 51of the first light transmissive layer 5 and the surface 61 of theoptical member 6 are directly bonded with using the normal temperaturebonding method. Specifically, the direct bonding is preferably performedby the surface-activated bonding, the atomic diffusion bonding, or thehydroxyl bonding.

(Forming Second Light Transmissive Layer on Optical Member)

As mentioned above, there is a case that a material of the opticalmember 6 is not uniform, and it is difficult to achieve 1 nm or less ofthe arithmetic average roughness Ra of in the surface 61 even if the CMPmethod or the like is applied. In this case, a second light transmissivelayer 9 in which a surface 91 is flattened, may be formed on the surface61 of the optical member 6 (refer to FIG. 7 ), and the optical member 6may be bonded to the first light transmissive layer 5 via the secondlight transmissive layer 9

Specifically, as illustrated in FIG. 11 , it is preferable to perform astep of forming the second light transmissive layer S81, and a step offlattening the second light transmissive layer S82 before the bondingstep S8 is performed.

(Step of Forming a Second Light Transmissive Layer)

As illustrated in FIG. 11 , the step of forming a second lighttransmissive layer S81 is a step wherein the second light transmissivelayer 9 having a light transmissive property is formed on the surface 61of the optical member 6 which is to face the first light transmissivelayer 5.

The second light transmissive layer 9 may be formed of the same materialwith the same method as those of the first light transmissive layer 5.The forming method of the second light transmissive layer 9 is notlimited to the method which is exemplified as that of the first lighttransmissive layer 5, but it may be, for example, a method wherein thesecond light transmissive layer 9 which has already been fabricated, isbonded to the optical member 6. Anyhow, since the step of forming thesecond light transmissive layer S81 is a separate step which isindependent of the light emitting element 4, this step may be performedemploying conditions suitable for the material without being subjectedto limitation of the forming conditions (for example, a temperature or abonding method). For example, the second light transmissive layer 9 maybe formed at a temperature of 400° C. or more, or may be bonded to theoptical member 6 at a temperature of 400° C. or more. Alternatively, thesecond light transmissive layer 9 may be bonded to the optical member 6with using the electric field.

The surface 61 of the optical member 6 on which the second lighttransmissive layer 9 is formed, may or may not be subjected to theroughening process or the flattening process. When the surface 61 isroughened, the total reflection can be suppressed, and thereby enhancingthe light extracting efficiency. When the refractive index of theoptical member 6 and the refractive index of the second lighttransmissive layer 9 are the same and the surface 61 is flattened, anoptical boundary face is not formed, whereby the Fresnel reflection canbe suppressed to enhance the light extracting efficiency. When any ofthose surface treatments is not applied to the surface 61, it canenhance the productivity, and lower the cost to manufacture the lightemitting device 1.

(Step of Flattening a Second Light Transmissive Layer)

As illustrated in FIG. 11 , a step of flattening a second lighttransmissive layer S82 is a step wherein a surface 91 of the secondlight transmissive layer 9 formed on the optical member 6 is flattened.

The second light transmissive layer may be flattened by, for example,the CMP method. It is preferable that the flattening is performed suchthat the arithmetic average roughness Ra of the surface 91 of the secondlight transmissive layer 9 becomes 1 nm or less. By flattening thesurface 91 of the second light transmissive layer 9, direct bonding canbe favorably made between the first light transmissive layer 5 and thesecond light transmissive layer 9, and the total reflection generateddue to the void at the interface between the second light transmissivelayer 9 and the first light transmissive layer 5 can be suppressed.

Subsequently, the surface 91 of the second light transmissive layer 9,which surface has been flattened, is brought into contact with the lightextracting surface 51 of the second light transmissive layer 5, whichsurface has been flattened, and then both are bonded together byperforming the above-mentioned bonding step S8.

According to this process, there can be obtained the light emittingdevice 1 which is configured to have the light emitting element 4/thefirst light transmissive layer 5/the second light transmissive layer9/the optical member 6.

(Step of Removing a Supporting Substrate)

As illustrated in FIGS. 11 and 12J, the step of removing a supportingsubstrate S9 is a step to wherein a supporting substrate 22 is removedtogether with the resin 21 (both are not illustrated in FIG. 12J, seeFIG. 12I) from the light emitting element 4 where the optical member 6is bonded.

For removing the supporting substrate 22, an adequate method may be usedaccording to the resin 21 used. While the step of removing a supportingsubstrate S9 may be performed at another timing in the manufacturingprocess, it is preferable to perform this step just before the cuttingstep S10, considering a strength and handleability of the light emittingelement 4 under manufacturing.

(Cutting Step)

As illustrated in FIGS. 11 and 12K, the cutting step S10 is a stepwherein the laminated structure in which the supporting substrate 22 hasbeen removed, is cut for chipping to manufacture the light emittingdevice 1. The chipping may be performed by the scribing or by thedicing. For example, if the chipping of the light emitting element 4 isperformed after the step of flattening a first light transmissive layer,only the optical member 6 is separated in the cutting step S10.

In the manufacturing method according to the present embodiment, it ispossible to manufacture the light emitting device 1 in which the lightextracting efficiency is enhanced, because of the suppression of thetotal reflection generated due to the difference of the refractive indexof the material, and the suppression of the total reflection generateddue to the void.

Although the light emitting device and the manufacturing method thereofaccording to the present disclosure is described above specifically bythe embodiment, the spirit of the present invention is not limited tosuch description, and it should be interpreted widely according to thedescription of the claims. It goes without saying that variousmodifications and alternations will be included in the spirit of thepresent invention.

The present disclosure may be applied to a light emitting device havinga high-efficiency LED or an LED that emits an ultraviolet light and amanufacturing method thereof. Such light emitting device may be used fora lighting device, a sterilizing device, a head ramp for vehicles, adisplay, a device of a sign advertising or the like.

As mentioned above, the light extracting efficiency can be enhanced inthe light emitting device according to the embodiment of the presentinvention since the first light transmissive layer is provided on onesurface, specifically on the light extracting surface side of thesemiconductor light emitting element, and the bonding surfaces of thisfirst light transmissive layer and the optical member are flat, and thefirst light transmissive layer and the optical member are directlybonded.

According to the manufacturing method of the light emitting deviceaccording to the embodiment of the present invention, the light emittingdevice in which the light extracting efficiency is enhanced can bemanufactured since the first light transmissive layer is formed on thelight extracting surface side of the semiconductor light emittingdevice, and the upper surface of the first light transmissive layer isflattened, and the flattened upper surface and the surface of theoptical member are directly bonded.

What is claimed is:
 1. A method for manufacturing a light emitting device comprising an optical member provided on a light extracting surface side of a semiconductor light emitting element via a first light transmissive layer and a second light transmissive layer, the method comprising steps of: (a) roughening said light extracting surface of said semiconductor light emitting element, (b) forming said first light transmissive layer on an entirety of said roughened light extracting surface, (c) flattening a surface of said first light transmissive layer that is on a side opposite said semiconductor light emitting element, (d) forming said second light transmissive layer on an entirety of a surface of said optical member, (e) flattening a surface of said second light transmissive layer that is on a side opposite said optical member, and (f) directly bonding said flattened surface of said first light transmissive layer and said flattened surface of said second light transmissive layer by performing surface-activated bonding, atomic diffusion bonding, or hydroxyl bonding.
 2. The method for manufacturing a light emitting device according to claim 1, further comprising: before the step (a), performing a step (g) of forming said semiconductor light emitting element on a growth substrate, performing a step (h) of removing said growth substrate from said semiconductor light emitting element formed on said growth substrate, and performing a step (i) of polishing a stripped surface of said semiconductor light emitting element that is exposed by the step (h), wherein: in the step (a), said polished stripped surface is roughened to form said light extracting surface.
 3. The method for manufacturing a light emitting device according to claim 1, wherein an arithmetic average roughness Ra of both of said flattened surface of said first light transmissive layer and said flattened surface of said second transmissive layer is 1 nm or less.
 4. The method for manufacturing a light emitting device according to claim 1, wherein said first light transmissive layer and/or said second light transmissive layer is formed of at least one inorganic dielectric material selected from the group consisting of SiO₂, SiON, TiO₂ and Al₂O₃, or an organic-inorganic hybrid material comprising at least one selected from the group consisting of SiO₂, SiON, TiO₂ and Al₂O₃, as an inorganic component.
 5. The method for manufacturing a light emitting device according to claim 1, wherein said first light transmissive layer and/or said second transmissive layer is formed of a material consisting essentially of Si, O, and N.
 6. The method for manufacturing a light emitting device according to claim 1, wherein a refractive index of said first light transmissive layer and/or a refractive index of said second light transmissive layer is in a range of 1.4 to 2.0.
 7. The method for manufacturing a light emitting device according to claim 1, wherein a difference between a refractive index of the first light transmissive layer and a refractive index of the optical member is in a range of ±0.3 based on absolute values of the refractive indexes of the first light transmissive layer and the optical member.
 8. The method for manufacturing a light emitting device according to claim 1, wherein said optical member is a fluorescent plate, a sapphire substrate, a GaN substrate or a lens.
 9. The method for manufacturing a light emitting device according to claim 1, wherein the optical member is inhomogeneous and comprises an inorganic material and fluorescent material particles, and wherein a first plurality of the fluorescent material particles are partially exposed from the inorganic material, and a second plurality of the fluorescent material particles are entirely embedded in the inorganic material.
 10. The method for manufacturing a light emitting device according to claim 1, wherein an arithmetic average roughness Ra of said surface of said optical member on which said second light transmissive layer is formed is greater than 1 nm.
 11. The method for manufacturing a light emitting device according to claim 1, further comprising: before the step (a), performing a step (j) of attaching a supporting substrate onto a side opposite to a light extracting surface side of said semiconductor light emitting element; and after the step (f), performing a step (k) of removing said supporting substrate.
 12. The method for manufacturing a light emitting device according to claim 1, further comprising: before the step (f), performing a chipping process.
 13. The method for manufacturing a light emitting device according to claim 11, wherein, in the step (a), said supporting substrate is attached onto a side opposite to light extracting surface sides of a plurality of semiconductor light emitting elements; and wherein the method further comprising, after the step (k), performing a step of cutting to separate the plurality of semiconductor light emitting elements into individual light emitting devices. 